The present invention relates to furnaces constructed of hearth and sidewall refractories, and more particularly relates to systems for the compressive binding of these refractories.
Furnaces are used extensively in the smelting and converting of ferrous and non-ferrous ores and concentrates. Furnaces of this type are generally circular or rectangular, having a bottom wall (hearth) and vertical walls comprised of refractory bricks and a roof or off gas hood. These furnaces are also characterized by a binding and support structure, the purpose of which is to maintain the refractory bricks of the hearth and walls in compression.
Adequate compression of the furnace walls, and particularly the hearth, is critical to maximize furnace campaign life and to prevent costly and potentially catastrophic furnace failure. During heating of the furnace to operating temperature, the individual bricks comprising the hearth and the walls expand, resulting in outward expansion of the hearth. Conversely, cooling of the furnace results in contraction of the individual bricks and overall shrinking of the furnace. If the compressive forces on the hearth or the walls are insufficient, gaps will be formed between the bricks during cooling phases of the furnace operation. These gaps can be infiltrated with molten metal or other material, resulting in permanent growth of the furnace. Repetition of heating and cooling cycles results in further incremental expansion of the furnace (known as xe2x80x9cratchetingxe2x80x9d), which usually results in a reduction of the furnace campaign life, by the potential for molten infiltration into the hearth refractory or excessive expansive forces exerted on the binding system.
In rectangular furnaces, the binding system usually consists of regularly spaced vertical beams known as xe2x80x9cbuckstaysxe2x80x9d, which are held together at the top and bottom by horizontal tie members extending across the furnace, the bottom tie members passing beneath the hearth and the upper tie members passing above the furnace roof. The structure of electric furnaces is discussed in more detail in Francki et al., Design of refractories and bindings for modem high-productivity pyrometallurgical furnaces, Non-Ferrous Metallurgy, Vol. 86, No. 971, pp. 112 to 118. Frequent adjustment of the tie members, as by loosening or tightening retaining nuts at the tie member ends, is necessary to maintain relatively constant compression on the refractories during thermal cycling of the furnace. The binding systems of most large rectangular furnaces in operation today are equipped with compression spring sets sized to maintain the desired compression on the brick work, thereby permitting some expansion and contraction of the furnace while maintaining the hearth under compression.
While spring sets permit some furnace movement, they do not eliminate the need for periodic adjustment of the spring loads to ensure that the forces on the tie members and the furnace hearth remain relatively constant during use of the furnace. Adjustment of the spring loads is performed with hydraulic jacking equipment, and is a difficult and unpleasant operation due the fact that the vicinity of the furnace is usually hot, dirty and ill-lit and because the adjustment screws on the spring sets usually become more difficult to turn with time. Therefore, the frequency of adjustment tends to be low and spring binding systems are often not used to their full advantage.
The problems with prior art adjustment systems are exemplified by U.S. Pat. No. 3,197,385 (Wethly), issued on Jul. 27, 1965. This patent relates to the use of hydraulic jacking equipment for adjustment of tie rod tension in a coke oven battery. According to Wethly, the tension in each tie rod is adjusted by a hydraulic tensioning jack which is mounted on the ends of the rods. However, the tensioning jack must be sequentially mounted on each tension rod to adjust the tension in the rods one by one, in sequence. In the sequential adjustment system taught by Wethly, it would be difficult to control the tension in the rods with any degree of precision since adjusting the tension in one rod will have an effect on the tension in neighboring rods. Furthermore, the sequential mounting and use of a hydraulic jack in close proximity to the furnace is an unpleasant task which is likely to be performed only when absolutely necessary, and therefore the frequency of adjustment is likely to be low.
Therefore, a need exists for improved furnace binding systems for both rectangular and circular furnaces. Preferably, such systems would permit the compressive forces on the refractory hearth and furnace walls to be accurately adjusted, and would permit adjustment of the compressive forces to be carried out remotely and continuously, thereby maximizing furnace life and improving safety.
The present invention overcomes the above-described problems of the prior art by providing a furnace binding and adjustment system in which the compressive forces on the furnace hearth can be accurately controlled and monitored on a continuous basis. The system of the invention includes fluid-pressurized tensioning or compression means for maintaining compressive forces on the hearth and/or furnace walls. The compressive forces applied to the furnace by the binding system are regulated by one or more pressure regulation means adapted to simultaneously or individually adjust the fluid pressure in one or more of the tensioning or compression means, thereby overcoming the problems in the prior art.
The control of the tensioning or compression means by one or more pressure regulation means is particularly well suited to remote operation, whereby a furnace operator situated in a control room can regulate the pressure in the pressure regulation means, thereby eliminating the need to carry out manual adjustments in the vicinity of the furnace. Furthermore, since the fluid pressure in the pressure regulation means and in the tensioning or compression means is proportional to the compressive forces exerted on the furnace, the binding system of the present invention permits accurate measurement and control of the compressive forces exerted on the furnace.